Use of a polyester polyether-type elastomer having a crystalline polyester such as polybutylene terephthalate (PBT) and polybutylene naphthalate (PBN) as a hard segment and a long chain aliphatic polyether polyol with a low glass transition temperature (Tg) such as polytetramethylene glycol (PTMG) as a soft segment for an electronic sealing material as a soft segment has been previously known (e.g., Patent Document 1) and the elastomer has already been practically used. However, since the ether bonds in the long chain aliphatic polyester polyol are susceptible to heat decomposition and hydrolysis, the elastomer is limited in its heat resistance, resistance to thermal aging, and water-proofness, and its application is limited.
On the other hand, a polyester polycarbonate-type elastomer using a polycarbonate as a soft segment has been known as an elastomer excellent in heat resistance, resistance to thermal aging, and water-proofness (see, for example, Patent Documents 2 and 3).